Turning food waste into energy in Los Angeles

Food waste should be regarded as a resource that is not yet being tapped. With that in mind, according to Waste360, the Los Angeles County Sanitation Districts have begun diverting food waste and turning it into methane, which can then be sold as biofuel. This approach uses infrastructure already available that is designed to create the biofuel.

The process works by converting food waste into a slurry with any contaminants removed at a recovery facility. Then the slurry is shipped to a plant which already uses biosolids to convert to methane using an anaerobic digestion system that takes three weeks. A ratio of 30 percent slurry made from food waste added to the biosolids can create twice as much methane as the biosolids on their own.

Currently, Los Angeles generates 4,000 tons of food waste per day. The new process can convert 165 tons per day with plans to increase that amount to as much as 550 tons of food waste per day by 2020. Some of the methane will be used to fuel vehicles designed to use biogas instead of ordinary gasoline; the rest will generate electricity in plants that burn natural gas.

The price of renewable natural gas is high right now. However, as the LACSD continues to scale up the operation, the price should continue to fall enough to become competitive with conventional natural gas.

Of course, methane is a greenhouse gas that, in some ways, is even more potent than carbon dioxide. One way to address that problem is to create power plants that capture the greenhouse gasses and either sequester them or, better, recycle them to create other useful products such as other kinds of biofuel or even carbon nanotubes. That way both the food waste problem is addressed and another source of renewable energy is created.

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